Preparation And Property Study Of Polymer-based Fluorescent Probes

In recent years, the preparation and application of nanoparticle-based fluorescent probes and polymer-based sensing membranes have attracted a wide attention in academic circles. As a kind of self-assembly nanoparticle, polymer micelles can provide fluorescent probes with special properties, such as water-solubility, biocompatibility, multifunctionality and high sensitivity; while sensing membranes have the advantages of convenient to use, handy and easy to recycle. Possessing these special properties and advantages, polymer micelle-based fluorescent probes and polymer sensing membranes are more suitable for practical application, and are expected to play the positive role in the fields of environmental detecting, bioscience, medical science and so forth.This paper studied the design and synthesis of rhodamine-based fluorescent probes for metal ions, which were further combined with amphiphilic copolymer and polymeric film to prepare micelle-based fluorescent probe and sensing membrane. The research works are mainly on two parts:1. R6GEDA was firstly synthesized from rhodamine 6G and ethylenediamine, which was further reacted with methacryloyl chloride in an ice bath to give the new functional monomer R6GEM. The structures of R6GEDA and R6GEM were confirmed by ¹H NMR, ¹³C NMR and ESI-MS. The change of UV-vis and fluorescence spectra indicated that R6GEM can response to Fe³⁺ selectively. Random amphiphilic copolymer P(NVP-co-R6GEM) was obtained from the free radical polymerization of R6GEM with vinyl pyrrolidone (NVP), its structure was demonstrated by FTIR and ¹H NMR, and the molecular weight was obtained from GPC. The amphiphilic copolymer can self-assemble into micelles as the result of the hydrophilic PVP segments and the hydrophobic R6GEM units in the polymer chain synchronously. The value of Critical Water Content (CWC) was 16.7vol.%. DLS revealed that the micelles had an average diameter of approximately 53 nm with a narrow size distribution in aqueous solution, and TEM showed the micelles were mostly spherical in shape and that the diameter was about 40 nm. The application of P(NVP-co-R6GEM) micelles as chemosensors for metal ions were investigated by UV-vis absorption and fluorescence spectroscopies. Upon addition of Fe³⁺ ions, a new absorption band at 533 nm and a novel emission peak at 553 nm appeared respectively, accompanied by the color change (from colorless to pink) and orange fluorescence emission of the micelle aqueous solution. The response of P(NVP-co-R6GEM) micelles to Fe³⁺ was reversible when excess ethylenediamine was added. Other common metal ions had no interference except for Hg²⁺, which had a slight effect. Possessing the water-solubility and biocompatibility, this micelle-based fluorescent probe can be used for water quality measuring and bioimaging etc.2. Firstly, R6GH was prepared by the reaction of rhodamine 6G with hydrazine hydrate. Then, a new rhodamine-based chemosensor R6GHS was synthesized from the Shiff Base reaction of R6GH with 4-(diethylamino) salicylaldehyde. The structures of R6GH and R6GHS were confirmed by ¹H NMR, ¹³C NMR and ESI-MS. R6GHS exhibits high sensitivity and selectivity for Cu²⁺ reversibly but no significant response toward other competitive metal ions in aqueous solution. Upon the addition of Cu²⁺, the spirolactam ring of R6GHS was opened and the solution color changed from colorless to pink in less than 1 min. Strangely, an unexpected fluorescence quenching was observed by excitation at 386 nm, which is contrary to the fluorescence turn-on of the most rhodamine-based chemosensors. But when the excitation wavelength was set at 512 nm, fluorescence enhancement of the chemosensor was observed. The likely novel sensing mechanism has been proposed. Sensing membranes were prepared by mixing R6GHS with PVC, and the optimum proportion of additive NaTPB was proved to be 4.67%. The sensing membranes can response to Cu²⁺ quickly at pH 6⁹ with the detection limit of 10^-7 mol·L^-1. This polymer-based handy sensing membrane can realize the fast detection anytime and anywhere with the potential of being applied in actual life.